I. Field
The present invention relates generally to communication, and more specifically to techniques for determining coverage for a terminal and switching between overlay communication systems.
II. Background
Wireless communication systems are widely deployed to provide various types of communication such as voice, packet data, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources. Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, and frequency division multiple access (FDMA) systems. A CDMA system may be designed to implement one or more standards such as IS-2000, IS-856, IS-95, W-CDMA, and so on. A cdma2000 system is a CDMA system that may implement IS-2000 and/or IS-856. A TDMA system may be designed to implement one or more standards such as Global System for Mobile Communications (GSM) and so on. A GSM system may implement General Packet Radio Service (GPRS) for packet data transmission. These various standards are well known in the art.
Some communication systems (e.g., such as those that implement IS-2000 W-CDMA, and GSM/GPRS) are capable of supporting voice and packet data services. Each type of service is characterized by a set of requirements. For example, voice service typically requires a fixed and common grade of service (GOS) for all users as well as relatively stringent and fixed delays. In contrast, packet data service may be able to tolerate different GOS for different users and may further be able to tolerate variable amounts of delays. To support both types of service, a communication system may first allocate system resources to voice users and then allocate any remaining system resources to packet data users whom can tolerate longer delays.
Some communication systems (e.g., such as those that implement IS-856) are optimized for packet data transmission, which is typically characterized by long periods of silence punctuated by large bursts of traffic. For an IS-856 system, a large portion of the system resources may be allocated to one user at a time, thereby greatly increasing the peak data rate for the user being served.
A service provider/network operator may deploy multiple communication systems to provide enhanced services for its subscribers. For example, a service provider may deploy one system capable of supporting both voice and packet data services for a large geographic area and may deploy another system capable of supporting packet data service for “hot spots” where packet data usage is expected to be high. The coverage areas of the two systems would typically overlap at least partially, and these systems would then be considered as “overlay” systems. A multi-mode/hybrid terminal may be able to receive service from one of the systems depending on its location and the desired service. Some of the challenges in such overlay systems include (1) determining the coverage bounds of the individual systems and (2) deciding when a terminal should switch between the systems.
There is therefore a need in the art for techniques to determine coverage for a terminal and to switch between overlay communication systems.